The present invention generally relates to the field of waveguides and, more particularly, to a waveguide bandpass filter having a non-contacting printed circuit filter assembly.
Conventional waveguide filters use elements that are in electrical and mechanical contact with the waveguide walls. Typical examples of these types of filters include inductive posts and inductive irises. These reactive elements are realized by means of metal rods or plates that are inserted into carefully machined openings and bonded to the walls of the waveguide by means of soldering, welding or compression techniques.
Newer printed circuit waveguide filters also use such elements printed on substrates that are held suspended between the waveguide walls with firm metallic contacts at the walls. These filters, known as fin-line filters, are simpler to make than inductive irises and posts but also require very precise machining to split the waveguide and cut the groove for supporting the substrate.
Because the above-described types of filters are in contact with the waveguide walls and because current flow in the junctions between the elements and the waveguide walls, and because of junction imperfections, the filter loss and reflection quality are often degraded. The waveguide filter of the application cross-referenced above overcomes the foregoing problems associated with conventional waveguide filters by providing a printed circuit filter element that does not require any contact with the waveguide walls.
This non-contacting printed circuit waveguide filter can be assembled by inserting a foam backed printed circuit within a short section of waveguide. The printed circuit is formed on a dielectric substrate which is positioned within the waveguide by means of dielectric foam spacer material. The filter facilitates very simple assembly techniques and eliminates practically all costly machining that is usually associated with waveguide filters. It also provides the highest attainable performance in terms of low losses and high reflection because the losses due to element contact resistance are eliminated.